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NACA-RM-A55G19
A study of conical camber for triangular and sweptback wings
Year: 1955
Abstract: INTRODUCTION
The total resistance of an airfoil may be considered as being composed of two separate components, the drag at zero lift and the drag associated with the production of lift. In the cruising condition the latter component can become a significant portion of the total drag of an airplane and, therefore, of considerable importance with regard to range.
The drag resulting from the development of lift may also be divided into two components, one associated with the viscous forces, that is, the skin-friction drag, and the other resulting from the pressure forces acting on the wing. The change in skin-friction drag with a change in lift results primarily from a movement of the boundary-layer transition point. This movement is, of course, caused by the pressure gradients acting over the lifting surface. On aircraft at full scale the boundary-layer is often turbulent over essentially the entire airplane surface; hence, the change in skin-friction drag with a change in lift coefficient is negligible. This*component must, therefore, be removed in wind-tunnel tests in order that proper estimates of the drag-due-to-lift characteristics can be made for full-scale aircraft. The other component of the drag due to lift, that due to pressure forces, may be estimated by thin-airfoil theory. Linear theory, however, predicts very large suction pressures at the leading edges of planar wings which give.rise to a force in the thrust direction. Since these pressures cannot be fully developed in a real fluid, a question arises as to how much of the leading-edge thrust can be obtained. Previous experimental investigations (refs. 1, 2, and 3) . have indicated that at transonic and supersonic speeds it is difficult to develop a significant portion of this leading-edge thrust for plane triangular wings-of small thickness (3 to 5 percent thick).
A theoretical study by Jones in reference 4 indicated that one way to attain an equivalent leading-edge thrust would be to-camber the wing leading edge. In this manner the suction pressures would be distributed over a relatively large area of the wing rather than concentrated at the airfoil leading edge. Thus, the magnitude of the pressures necessary to 5, achieve the equivalent of full leading-edge suction would be physically possible.
The initial results of a study directed at determining a cambered surface for triangular wings which would provide an equivalent leading-edge thrust were presented in reference 1. The study showed that incorporation of a conical type of camber in an aspect-ratio-2 triangular wing resulted in substantial reductions in drag due to lift in the cruise lift-coefficient range at transonic speeds.
It is the purpose of the present report to elaborate on the analytical method for deriving conical camber for transonic and supersonic speeds for wings of triangular and sweptback plan form. The report also contains experimental data showing the effects of conical camber on the lift, drag, and pitching moment characteristics of low-aspect-ratio triangular and sweptback wings at subsonic and supersonic speeds. Comparison of measured drag polars with those computed from lifting-surface theory are made to determine the effectiveness of the design methods.
The total resistance of an airfoil may be considered as being composed of two separate components, the drag at zero lift and the drag associated with the production of lift. In the cruising condition the latter component can become a significant portion of the total drag of an airplane and, therefore, of considerable importance with regard to range.
The drag resulting from the development of lift may also be divided into two components, one associated with the viscous forces, that is, the skin-friction drag, and the other resulting from the pressure forces acting on the wing. The change in skin-friction drag with a change in lift results primarily from a movement of the boundary-layer transition point. This movement is, of course, caused by the pressure gradients acting over the lifting surface. On aircraft at full scale the boundary-layer is often turbulent over essentially the entire airplane surface; hence, the change in skin-friction drag with a change in lift coefficient is negligible. This*component must, therefore, be removed in wind-tunnel tests in order that proper estimates of the drag-due-to-lift characteristics can be made for full-scale aircraft. The other component of the drag due to lift, that due to pressure forces, may be estimated by thin-airfoil theory. Linear theory, however, predicts very large suction pressures at the leading edges of planar wings which give.rise to a force in the thrust direction. Since these pressures cannot be fully developed in a real fluid, a question arises as to how much of the leading-edge thrust can be obtained. Previous experimental investigations (refs. 1, 2, and 3) . have indicated that at transonic and supersonic speeds it is difficult to develop a significant portion of this leading-edge thrust for plane triangular wings-of small thickness (3 to 5 percent thick).
A theoretical study by Jones in reference 4 indicated that one way to attain an equivalent leading-edge thrust would be to-camber the wing leading edge. In this manner the suction pressures would be distributed over a relatively large area of the wing rather than concentrated at the airfoil leading edge. Thus, the magnitude of the pressures necessary to 5, achieve the equivalent of full leading-edge suction would be physically possible.
The initial results of a study directed at determining a cambered surface for triangular wings which would provide an equivalent leading-edge thrust were presented in reference 1. The study showed that incorporation of a conical type of camber in an aspect-ratio-2 triangular wing resulted in substantial reductions in drag due to lift in the cruise lift-coefficient range at transonic speeds.
It is the purpose of the present report to elaborate on the analytical method for deriving conical camber for transonic and supersonic speeds for wings of triangular and sweptback plan form. The report also contains experimental data showing the effects of conical camber on the lift, drag, and pitching moment characteristics of low-aspect-ratio triangular and sweptback wings at subsonic and supersonic speeds. Comparison of measured drag polars with those computed from lifting-surface theory are made to determine the effectiveness of the design methods.
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| contributor author | NASA - National Aeronautics and Space Administration (NASA) | |
| date accessioned | 2017-09-04T17:45:15Z | |
| date available | 2017-09-04T17:45:15Z | |
| date copyright | 01/01/1955 | |
| date issued | 1955 | |
| identifier other | EIMCWDAAAAAAAAAA.pdf | |
| identifier uri | http://yse.yabesh.ir/std/handle/yse/168377 | |
| description abstract | INTRODUCTION The total resistance of an airfoil may be considered as being composed of two separate components, the drag at zero lift and the drag associated with the production of lift. In the cruising condition the latter component can become a significant portion of the total drag of an airplane and, therefore, of considerable importance with regard to range. The drag resulting from the development of lift may also be divided into two components, one associated with the viscous forces, that is, the skin-friction drag, and the other resulting from the pressure forces acting on the wing. The change in skin-friction drag with a change in lift results primarily from a movement of the boundary-layer transition point. This movement is, of course, caused by the pressure gradients acting over the lifting surface. On aircraft at full scale the boundary-layer is often turbulent over essentially the entire airplane surface; hence, the change in skin-friction drag with a change in lift coefficient is negligible. This*component must, therefore, be removed in wind-tunnel tests in order that proper estimates of the drag-due-to-lift characteristics can be made for full-scale aircraft. The other component of the drag due to lift, that due to pressure forces, may be estimated by thin-airfoil theory. Linear theory, however, predicts very large suction pressures at the leading edges of planar wings which give.rise to a force in the thrust direction. Since these pressures cannot be fully developed in a real fluid, a question arises as to how much of the leading-edge thrust can be obtained. Previous experimental investigations (refs. 1, 2, and 3) . have indicated that at transonic and supersonic speeds it is difficult to develop a significant portion of this leading-edge thrust for plane triangular wings-of small thickness (3 to 5 percent thick). A theoretical study by Jones in reference 4 indicated that one way to attain an equivalent leading-edge thrust would be to-camber the wing leading edge. In this manner the suction pressures would be distributed over a relatively large area of the wing rather than concentrated at the airfoil leading edge. Thus, the magnitude of the pressures necessary to 5, achieve the equivalent of full leading-edge suction would be physically possible. The initial results of a study directed at determining a cambered surface for triangular wings which would provide an equivalent leading-edge thrust were presented in reference 1. The study showed that incorporation of a conical type of camber in an aspect-ratio-2 triangular wing resulted in substantial reductions in drag due to lift in the cruise lift-coefficient range at transonic speeds. It is the purpose of the present report to elaborate on the analytical method for deriving conical camber for transonic and supersonic speeds for wings of triangular and sweptback plan form. The report also contains experimental data showing the effects of conical camber on the lift, drag, and pitching moment characteristics of low-aspect-ratio triangular and sweptback wings at subsonic and supersonic speeds. Comparison of measured drag polars with those computed from lifting-surface theory are made to determine the effectiveness of the design methods. | |
| language | English | |
| title | NACA-RM-A55G19 | num |
| title | A study of conical camber for triangular and sweptback wings | en |
| type | standard | |
| page | 82 | |
| status | Active | |
| tree | NASA - National Aeronautics and Space Administration (NASA):;1955 | |
| contenttype | fulltext |